Fabrication of semiconductor devices typically includes an implantation of ions for various purposes known to those skilled in the art. In an ideal implantation without error, an ion beam will be directed normal to a plane defined by a substrate or wafer surface. It will be appreciated by those skilled in the art that angled implants are sometimes done intentionally, but it is the unintentional angle error that the present disclosure is intended to address, as these implants are undesirable. However, it will also be appreciated that the disclosure herein can easily be extended to measure error in angled implants.
However, variations in direction of ion implantation can occur. Ion beam angle error in ion implantation, particularly at the source/drain extension (SDE) step, can cause xtor parametric variation, depressed MPY, and Channel Hot Carrier (CHC) degradation, thereby degrading transistor performance and reducing product yield. It is therefore important to monitor and control ion beam angle. The SDE step may be the most sensitive step but product can be affected by angle error in other implant steps as well.
Methods for measuring an angle of an ion beam with respect to a substrate are known. These methods include crystal channeling or use of transistors. However, wafer-based methods of measuring ion implantation angle which rely on crystal channeling are not sensitive for low energy or amorphizing implants. Further, methods which use transistors are expensive and time consuming. Until now, there has been no know method of detecting angle error in low energy SDE implants, except for fabricating transistors and measuring parametrics weeks after the implants have been completed.
Accordingly, there is a need to solve these and other problems of the prior art by detecting ion implantation angle variations with high sensitivity. Further, there is a need for a method that is applicable in numerous applications, including low energy and amorphizing implants and across a wide range of species, energies, and doses; using relatively simple processing, and without the need to fabricate transistors.